Arc tube having particular volume and gas pressure for luminous flux

Abstract

An arc tube for a discharge lamp unit which emits light which is suitable in luminous flux, color temperature, and chromaticity. The arc tube is composed of a closed glass ball in which electrodes confront one another and which is sealingly charged with light emitting materials, namely, mercury and a metal iodide of NaI and ScI 3 groups together with Xe inert gas. In accordance with the invention, the closed glass ball has a volume of 20 to 50 μl, the density of the mercury in the closed glass ball is in a range of 2×10 -2 to 4×10 -2 mg/μl, the density of the metal iodide is in a range of 6×10 -3 to 12×10 -3 mg/μl, and the charged Xe gas pressure is 3 to 6 atm. These ranges make it possible to readily manufacture on a large scale arc tubes which are substantially equal in performance, being substantially uniform in tube voltage, luminous flux, color temperature and chromaticity.

What is claimed is: 
     
       1. In an arc tube for a discharge lamp unit comprising a closed glass ball in which electrodes confront one another and which is sealingly charged with light emitting materials, including mercury and a metal iodide of NaI and ScI 3  groups together with Xe inert gas, the improvement comprising: said closed glass ball having a volume in a range of 20 to 50 μl,   said mercury in said closed glass ball having a density in a range of 2×10 -2  to 4×10 -2  mg/μl,   said metal iodide in said closed glass ball having a density in a range of 6×10 -3  to 12×10 -3  mg/μl, and   a charged gas pressure of said Xe inert gas being in a range of 3 to 6 atm.